Patent GB-1324837-A (GB)
Title: Negative voltage regulator adapted to be constructed as an integrated circuit
IPC: G05F1/56
Filed: 1971-04-28
Abstract: 1324837 Automatic voltage control; automatic voltage and current regulation MOTOROLA INC 28 April 1971 [8 May 1970] 11817/71 Headings G3R and G3X  A D. C. voltage regulator for controlling the negative supply 12 to a load 28 comprises a series transistor 166 controlled by a differential amplifier formed by transistors 136, 138 whose bases respectively receive the load voltage and a reference voltage which is derived from a temperature compensated reference voltage generator 59 and a voltage shifter connected in a non-loading manner thereto. The generator 59 comprises two parallel branches respectively comprising a Zener-diode 58 having a positive temperature co-efficient of voltage and series-connected diodes and resistors of which the diodes 64, 70, 72 have a negative temperature co-efficient of voltage and the resistors 66, 68, 74 have a positive temperature co-efficient of resistance. The voltage from the generator 59 is applied to the base of a transistor 98, the connection of these two members and that of transistor 98 to transistor 100 ensuring that the generator 59 is substantially unloaded. These two transistors, together with the transistors 102, 110, form a balanced differential amplifier having the same voltage at the bases of transistors 98, 110, which voltage is changed to the reference voltage by an amplifying loop comprising members 102, 110, 112, 114, 120, 18 and 24. The amplified voltage at the emitter of transistor 120 is determined by the ratio of the resistors 18, 24 which can thus be chosen to determine the reference voltage applied to transistor 136. Operation of the amplifying loop is explained with particular reference to members 36, 116 which prevent the generation of oscillations and, in conjunction with the high collector impedance of transistor 112, provide filtering of the noise produced by the Zener-diode 58. Operation of the differential amplifier 136, 138 is also explained with particular reference to the action of the load 28 and capacitor 34 in preventing oscillations in the amplifying loop composed of members 136, 138, 118, 158 and 166. Capacitor 174 and the high impedance at the base of transistor 158 serve to stabilize this amplifier. Each of the transistors 50, 52, 104, 122, 126, 148, 142, 152 and 162 functions as a constant current source by virtue of the circuit arrangement comprising members 52, 60, 76; 78, 80, 84, 90, 92, 94, 96, in which the voltage across resistor 78 is approximately equal to that across resistor 74, the current through the resistor 78 is constant and independent of temperature, the voltage across resistor 96 is approximately equal to the voltage across each of the resistors 62, 86, 106, 124, 128, 150, 144, 154, 164, and the current through the latter resistor is independent of temperature by virtue of the temperature independence of the current through the resistor 96. The temperature-independence of the collector current of transistor 50, together with the constant current in resistor 74, ensures constant current through the Zener-diode 58. Connection of transistor 90 to the base supply lead 51 avoids loading the network 92, 94, 96, since current variation in the lead 51 is divided by the beta of transistor 90 when fed back therethrough to this network. The connection of transistors 76, 84 ensures constant collector current in the latter transistor despite variations of its beta. Operation of the two differential amplifiers 98, 100, 102, 110 and 136, 138 is unaffected by variations of their common reference voltage across the resistor 96, the current through the resistors 108, 156 respectively associated with these amplifiers being maintained constant by the action of relevant ones of the transistors 112, 118, 119 and the constant current transistors 50 ---- 162. The latter transistors and the transistors 84, 90, 118 are arranged to have a low base impedance and a high collector impedance to assist the capacitors 34, 36 in reducing the ripple voltage in the supply to the terminals 12. The connections of certain of these transistors are discussed with reference to this aspect of the regulator operation. If the current taken by the load 28 exceeds a predetermined value, the voltage across a resistor 14 plus the base emitter forward voltage drops of the transistor 158, 166 exceeds the forward voltage threshold of four diodes 160, 168, 170, 172, thus controlling the transistors 158, 166 to operate in a current limiting manner. In addition to this excess current protection, short circuiting of the load 28 causes a diode 132 and transistor 130 to be made conductive, thus controlling the transistor 120 to supply the constant current source 122 and so reduce the voltage across the resistors 18, 24 to zero. This action protects the transistors 136, 138 by ensuring that the maximum voltage which appears across their bases is equal to the forward voltage drop across the diode 132 plus the base emitter voltage drop across the transistor 130. Diode 132 prevents forward bias of the base collector junction of the transistor 130 due to the base emitter voltage drop of the transistor 120. Automatic start of the regulator when connected to the negative supply 12 is provided by the circuit components 44, 48, 56, 60, 74, 76, 78, 80, 84, 90 and 96, a typical starting operation being described and involving the breakdown of the Zener-diode 44 when the supply is connected and the subsequent conduction of the various transistors of which the last (transistor 90) turns on the transistor 50 ----- 162 to put the regulator into a permanently-on condition. Automatic turn-off of the regulator is achieved by applying, at terminal 40, a negative voltage to the base of transistor 82, whose subsequent conduction turns off the transistor 84 and thus causes all the voltages in the regulator to fall to zero (excluding the start circuit). Diode 134 bypasses the transistors 136, 138 to prevent damage to the transistor 136 during automatic turn-off. The components within the rectangle 10 are formed as an integrated circuit. If the load 28 is at a distance from the regulator separate leads from terminals 30, 32 are provided.